Field of the Invention
The present invention relates in general to mechanical manipulators and appendages for use in robotics applications.
The Prior Art
The mechanical manipulator of an industrial robot is commonly implemented as a serial link structure utilizing revolute joints. The links are the rigid members coupled to each other by the joints. The joints (also called axis) are the movable components of the robot that enable relative motion between adjacent links.
Joint rotation is usually powered by motors, hydraulics or pneumatic actuators. In larger mechanical manipulators, these actuators can be directly connected to or within the joint to directly impart torque when actuated. When mechanical manipulators get very small, such as in use for “fingers” in mechanical hands, providing the motors, hydraulics and pneumatics directly attached to the joint is impractical due to size constraints and mass impacts on the moment of inertia. An alternative that is widely used is to utilize cables as artificial tendons that transfer the rotational force back to remotely located actuation such as a motor or pneumatic actuator.
When cables are used in mechanical manipulators, the cables need to be routed through the links and joints to the remotely located actuators. The cables may move in the links and joints when the mechanical manipulators are moving. The cables pass through the links and joints and may change direction at various points. At these points where the direction of the cable must change, it is important to reduce friction as much as possible to minimize wear and maximize resulting forces through the cable.
Routing tension cables in mechanical manipulators as described above requires overcoming friction while directing the path of the cable throughout any rotation of the links. There are three primary solutions for routing tension cables in mechanical manipulators: pulley based systems, the use of a Bowden cable or routing the cable over pins and bearings.
A very low friction configuration utilizes pulleys to route the cables. However, because a pulley is required wherever a cable must change direction, this can result in a large number of pulleys, which are mechanically complicated to implement, have high costs, and consume significant volume. In addition, if the cable falls off the pulley, the system has broken.
A more common configuration utilizes a Bowden cable, which is a cable mechanism utilizing a thin stranded cable that moves inside of a flexible outer housing. A Bowden cable provides an easy mechanism to route a cable through a confined area with little regard to position and obstacles. However, Bowden cables are relatively high friction and their performance degrades significantly over time.
Another common configuration is to run cables over metal pins or bearing races. This approach generally does not provide adequate alignment of the cable and can allow rubbing of the cable against the body of the link. This can result in high friction and wear in the mechanical manipulator reducing performance and operating lifetime.
Many other mechanical systems utilize cables to transmit tension between moving parts unrelated to link and joint based movement. These systems may experience similar challenges to those described above including: friction, wear, cost, and weight.
Ceramic guides have been widely used in the textile industry to route thread and yarn through machines. The primary reason for using ceramic guides has been to reduce lint build-up in textile factories.
Ceramic guides are used in fishing rods to reduce wear on the fishing line and rod.